U.S. patent number 5,842,060 [Application Number 08/813,269] was granted by the patent office on 1998-11-24 for illumination device with curved beam splitter for illumination an object with continuous diffuse light.
This patent grant is currently assigned to Northeast Robotics LLC. Invention is credited to Steven M. LeBlanc, Timothy P. White.
United States Patent |
5,842,060 |
White , et al. |
November 24, 1998 |
Illumination device with curved beam splitter for illumination an
object with continuous diffuse light
Abstract
An illumination device for illuminating an object to be
observed, by a machine vision camera or the like for example, with
a continuous diffuse wide angle light which is supplied along the
observation axis of the machine vision camera. The illumination
device contains a light source to illuminate a curved beam splitter
and a diffuser is located therebetween. The diffuser is mounted
inclined with respect to the observation axis and the curved beam
splitter minimizes the height of the illumination source and
facilitates supplying a more uniform field of illumination to the
object to be observed. The inclined diffuser only indirectly
illuminates of the object to be observed.
Inventors: |
White; Timothy P. (New Boston,
NH), LeBlanc; Steven M. (Philadelphia, PA) |
Assignee: |
Northeast Robotics LLC (Weare,
NH)
|
Family
ID: |
46252512 |
Appl.
No.: |
08/813,269 |
Filed: |
February 14, 1997 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
501213 |
Jul 11, 1995 |
5604550 |
|
|
|
331882 |
Oct 31, 1994 |
5539485 |
|
|
|
Current U.S.
Class: |
396/155; 396/200;
362/16; 362/291; 348/86; 362/296.09 |
Current CPC
Class: |
H05K
13/0812 (20180801); G01N 21/8806 (20130101); H04N
5/2256 (20130101); G03B 15/03 (20130101); G03B
27/323 (20130101) |
Current International
Class: |
G01N
21/88 (20060101); H05K 13/08 (20060101); G03B
15/03 (20060101); H05K 13/00 (20060101); G03B
015/06 () |
Field of
Search: |
;348/131,86,87,88-95,270
;396/4,155,200 ;362/3,16-18,290-291,296 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gray; David M.
Attorney, Agent or Firm: Davis and Bujold
Parent Case Text
This is a Continuation-In-Part of application Ser. No. 08/501,213
filed Jul. 11, 1995 now U. S. Pat. No. 5,604,550 which is a
Continuation-In-Part of application Ser. No. 08/331,882 filed Oct.
31, 1994 now U.S. Pat. No. 5,539,485.
Claims
What is claimed is:
1. An illumination device for illuminating an object to be observed
by a camera along an observation axis extending from the camera to
the object, said illumination device comprising:
a housing having at least a first aperture therein alignable with
an observation axis;
a partially reflective beam splitter being supported by said
housing and being positioned obliquely relative to the observation
axis adjacent said at least first aperture;
a light source being arranged to cast light on a first surface of
said beam splitter;
a diffuser being positioned between said beam splitter and said
light source for diffusing light from said light source as the
light passes through said diffuser to said first surface of said
beam splitter;
wherein said partially reflective beam splitter is a curved member
and said diffuser is sufficiently partially inclined with respect
to the observation axis so as only to be able, during use, to
indirectly illuminate a desired portion of the object to be
observed, via said curved beam splitter, when the object is
positioned along the observation axis thereby facilitating
generation of a substantially uniform illumination field even when
the illumination device is located adjacent the object to be
observed.
2. The illumination device according to claim 1, wherein a first
elongate straight edge portion of said curved beam splitter forms a
first angle with respect to said observation axis and a second
opposed elongate straight edge portion of said beam splitter forms
a second different angle with respect to said curved beam
splitter.
3. The illumination device according to claim 1, wherein said first
aperture of said housing defines a clear aperture of an inspection
system and the radius of curvature of said curved beam splitter is
between about 1 to about 3 times the minimum clear aperture
dimension.
4. The illumination device according to claim 1, wherein said
housing has a second aperture therein which is also alignable with
said observation axis and said beam splitter is located between
said first aperture and said second aperture.
5. The illumination device according to claim 1, wherein said light
source comprises one of a bulb, an incandescent fiber optic, at
least one LED, a fluorescent light and an array of lights.
6. The illumination device according to claim 1, wherein said
illumination device includes a light trap and said light trap is
positioned such that unreflected diffused light, from said light
source, which passes through said curved beam splitter is absorbed
by said light trap.
7. The illumination device according to claim 1, wherein the inner
surface of the housing is coated with a substance which reflects a
sufficient amount of light so as to match a brightness of the
diffused light reflected by said curved beam splitter from said
diffuser toward the object to be observed.
8. The illumination device according to claim 1, wherein said
illumination device is used in combination with an inspection
camera, and said inspection camera is positioned along said
observation axis and adjacent a second aperture of said housing to
sense light reflected by the object to be observed and passing
through said curved beam splitter.
9. The combination according to claim 8 wherein the combination
further includes a computer and assembly equipment, and the
computer is connected with said inspection camera and the assembly
equipment to control and manipulate the object to be observed, as
desired.
10. An inspection system for illuminating an object to be observed
by a camera along an observation axis extending from the camera to
the object; said inspection system including an illumination device
comprising:
a housing having at least a first aperture therein alignable with
an observation axis;
a partially reflective beam splitter being supported by said
housing and being positioned obliquely relative to the observation
axis adjacent said at least first aperture;
a light source being arranged to cast light on a first surface of
said beam splitter;
a diffuser being positioned between said beam splitter and said
light source for diffusing light from said light source as the
light passes through said diffuser to said first surface of said
beam splitter;
wherein said partially reflective beam splitter is a curved member
and said diffuser is sufficiently partially inclined with respect
to the observation axis so as only to be able, during use, to
indirectly illuminate a desired portion of the object to be
observed, via said curved beam splitter, when the object is
positioned along the observation axis thereby facilitating
generation of a substantially uniform illumination field even when
the illumination device is located adjacent the object to be
observed.
11. The inspection system according to claim 10, wherein said
housing has a second aperture therein also aligned with said
observation axis and said curved beam splitter is located between
said first aperture and said second aperture; and
said light source comprises one of a bulb, and incandescent fiber
optic, at least one LED and a fluorescent light.
12. The inspection system according to claim 10, wherein said first
aperture of said housing defines a clear aperture of an inspection
system and the radius of curvature of said curved beam splitter is
between about 1 to about 3 times the minimum clear aperture
dimension; and a first elongate straight edge portion of said
curved beam splitter forms a first angle with respect to said
observation axis and a second opposed elongate straight edge
portion of said beam splitter forms a second different angle with
respect to said curved beam splitter.
13. The inspection system according to claim 10, wherein said
illumination device includes a light trap and said light trap is
positioned such that unreflected diffused light, from said light
source, which passes through said curved beam splitter is absorbed
by said light trap.
14. The inspection system according to claim 10, wherein the inner
surface of the housing is coated with a substance which reflects a
sufficient amount of light so as to match a brightness of the
diffused light reflected by said curved beam splitter from said
diffuser toward the object to be observed.
15. A method of illuminating an object to be observed by a camera
along an observation axis extending from the camera to the object,
said method comprising the steps of:
utilizing a housing having two aligned apertures therein which are
both aligned with an observation axis;
supporting a partially reflective curved beam splitter within said
housing between said apertures and along the observation axis
adjacent;
arranging a light source to cast light on a first surface of said
beam splitter;
positioning a diffuser, at least partially inclined with respect to
said observation axis, between said curved beam splitter and said
light source for diffusing light from said light source as the
light passes through said diffuser to said curved beam
splitter;
supply light, from said light source, through said diffuser to said
curved beam splitter;
reflecting a portion of said light, via said curved beam splitter,
toward the object to be observed;
allowing a portion of light reflected back by said object to be
observed to pass through said curved beam splitter and be sensed by
said camera whereby said diffuser is sufficiently inclined with
respect to the observation axis so as only to be able, during use,
to indirectly illuminate a desired portion of the object to be
observed, via said curved beam splitter, when the object is
positioned along the observation axis.
16. The method according to claim 15, further comprising the steps
of forming a first angle between a first elongate substantially
straight edge portion of said curved beam splitter and said
observation axis and forming a second angle between a second
opposed elongate substantially straight edge portion of said beam
splitter and said curved beam splitter with said second angle being
different from said first angle.
17. The method according to claim 15, wherein said first aperture
of said housing defines a clear aperture of an inspection system
and said method further comprising the step of selecting the radius
of curvature of said curved beam splitter to be between about 1 to
about 3 times the minimum clear aperture dimension.
18. The method according to claim 15, further comprising the step
of utilizing one of a bulb, an incandescent fiber optic, at least
one LED and a fluorescent light as said light source.
19. The method according to claim 15, further comprising the steps
of providing a light trap and positioning said light trap such that
unreflected diffuse light which passes through said curved beam
splitter is absorbed by said light trap.
20. The method according to claim 15, further comprising the steps
of coating an inner surface of the housing with a substance which
reflects a sufficient amount of light so as to match a brightness
of the diffused light reflected by said curved beam splitter from
said diffuser toward the object to be observed.
Description
FIELD OF THE INVENTION
This invention pertains to an illumination device for illuminating
an object to be observed, by a machine vision camera or the like
for example, with a continuous diffuse wide angle light whose
illumination is supplied both along the viewing axis of the machine
vision camera and off axis and includes a curved beam splitter
which minimizes the height of the illumination source and provide a
more uniform field of illumination to the object to be
observed.
BACKGROUND OF THE INVENTION
Robotics assembly machines often utilize video cameras to observe
the component, part or work piece being handled, machined or
assembled. For instance, in the assembly of electronic components,
the chips or wafers are often assembled into printed circuit boards
by robots utilizing video cameras to position the components and/or
to inspect the assembled device for defects throughout the
process.
In the microelectronics industry, solder pads on surface-mount
devices are often observed by machine vision systems for assembly
and manufacturing purposes. The accuracy and reliability of a
machine vision system is critical for proper alignment of the
numerous components which are to be mounted on a printed circuit
board. For optimum alignment, solder pads must be clearly observed
in high contrast with their background.
Components in many industries often utilize etched characters
appearing on mirror like surfaces that serve to identify the
components and to accurately position them during assembly. In
order to permit a clear image of the characters to be produced in
the camera for accurate manipulation of the parts by the robotics
handling equipment, it is important that the observed object be
properly illuminated.
Proper illumination of many different shiny and uneven surfaces,
e.g. solder connections, foil packaging, ball bearings, etc., is
critical if high quality robotics assembly is to be achieved.
However, such shiny and uneven surfaces are difficult to illuminate
for accurate video imaging, and this creates a need for improved
illumination of such objects being observed by machine vision
cameras.
When using previously available illumination systems to illuminate
work pieces having uneven, highly reflective surfaces, the uneven
reflection of light from these surfaces frequently produces
erroneous images and signals when viewed through the camera thereby
possibly resulting in an erroneous signal or incorrect/inaccurate
measurement. Errors of one or two thousands of an inch in a
fiducial location measurement for a single component are sufficient
to ruin a large and expensive circuit board. Furthermore,
previously available illumination systems for robotics handling of
items have not produced a light which is uniform over the entire
object being observed. As a result, the reflected image suffers
from erroneous shadows, glints and glare thereby rendering it
difficult to determine the precise location or quality of the
object.
To date, many illumination devices have been developed to provide
substantially uniform illumination of an object to be viewed, but
such known illumination devices are fairly large and cumbersome and
are thus difficult to integrate into an electronic manufacturing
process. For example, one of the Inventor's known light system
might occupy a volume of 300 cubic inches and weigh several pounds,
thereby adding to the costs and expense in constructing machine
vision equipment in a very competitive industry. It is desirable to
manufacture a miniature illumination device which may occupy 8
cubic inches or less and only weigh a few ounces. Such
miniaturization allows significant cost savings and lessens the
expense of the machinery for inspecting manufactured products.
The term "diffuse", as used in this specification and appended
claims, means a light source which is uniformly dispersed over a
broad range of incident angle of azimuth and elevation with respect
to the object being observed, and the light source approaches
complete coverage over the area where the light is directed, i.e.
greater than 80% of the possible angular range of incident
light-approaching area X in FIG. 12. The term "concealed", as used
in this specification and appended claims, when referring to the
diffuser and the object to be observed, means that the surface
emitting the diffused light from the diffuser is positioned such
that the emitting surface of the diffuser can not directly
illuminate the object, i.e. only indirect illumination of the
object by reflection of light off the beam splitter or the side
wall(s) of the housing or supplying light through the beam splitter
can occur.
SUMMARY OF THE INVENTION
Wherefore it is an object of the invention to overcome the above
noted drawbacks of the prior art illumination devices.
It is another object of the present invention to develop an
improved continuous diffuse illumination device for machine vision
systems having a simplistic design which precisely determines the
location of the object being observed.
It is a further object of the invention to develop an improved
diffuse wide angle illumination field to improve image quality and
uniformity of appearance of uneven specular surfaces, such as those
found in the electronic and pharmaceutical manufacturing processes,
e.g. circuit boards, components, pills, capsules, and their
packaging.
A still further object of the invention is to provide an
illumination arrangement that increases the uniformity of the
illumination provided thereby and achieves a substantially
symmetrical illumination geometry.
Yet another object of the invention is to increase (e.g. double)
the brightness of the light reflected by the beam splitter to make
such reflected light appear more equal in brightness to the light
reflected by the diffusely reflecting inner surfaces of the
surrounding housing structure.
A further another object of the invention is to minimize the
brightness of the direct light from the diffuser to the object to
the same range of brightness as the light reflected by the beam
splitter and the surrounding housing structure.
Still another object of the invention is to minimize uneven
illumination of the object to be observed and the area adjacent the
object, e.g. maximize the range of elevational angles of incident
which commonly occur with simple beam-splitter illumination devices
(e.g. Carr et al. (U.S. Pat. No. 3,944,336) for example) where the
beam splitter is planar and its bottom edge is substantially flush
with the bottom aperture of the housing.
Another object of the invention is to space the diffuser a
sufficient distance from the opening or incline the diffuser so
that, in use, the diffuser is completely invisible to the object
being observed whereby direct illumination of the diffuser of the
object by the diffuser is prevented by the housing for the
diffuser.
A further object of the invention is to simplify the design of the
diffuser and thereby reduce the amount of material required to
manufacture the diffuser as well as the time, cost and production
in machining and/or forming an necessary angle required of the
diffuser.
A still further object of the invention is to minimize or eliminate
any direct illumination of the object being observed by the
diffuser to facilitate even illuminate of the object being
imaged.
Still another object of the invention is to utilize a curved beam
splitter to minimize the height of the illumination source and
provide a more uniform field of illumination to the object to be
observed.
These and other objects of the invention are realized by an
illumination device for illuminating an object to be observed by a
camera along an observation axis extending from the camera to the
object, said illumination device comprising: a housing having at
least a first aperture therein alignable with an observation axis;
a partially reflective beam splitter being supported by said
housing and being positioned obliquely relative to the observation
axis adjacent said at least first aperture; a light source being
arranged to cast light on a first surface of said beam splitter; a
diffuser being positioned between said beam splitter and said light
source for diffusing light from said light source as the light
passes through said diffuser to said first surface of said beam
splitter; wherein said partially reflective beam splitter is a
curved member and said diffuser is sufficiently inclined with
respect to the observation axis so as only to be able, during use,
to indirectly illuminate a desired portion of the object to be
observed, via said curved beam splitter, when the object is
positioned along the observation axis thereby facilitating
generation of a substantially uniform illumination field even when
the illumination device is located adjacent the object to be
observed.
The invention also relates to an illumination device for
illuminating an object to be observed by a camera along an
observation axis extending from the camera to the object; said
illumination device comprising: a housing having at least a first
aperture therein alignable with an observation axis; a partially
reflective beam splitter being supported by said housing and being
positioned obliquely relative to the observation axis adjacent said
at least first aperture; a light source being arranged to cast
light on a first surface of said beam splitter; a diffuser being
positioned between said beam splitter and said light source for
diffusing light from said light source as the light passes through
said diffuser to said first surface of said beam splitter; wherein
said partially reflective beam splitter is a curved member and said
diffuser is sufficiently inclined with respect to the observation
axis so as only to be able, during use, to indirectly illuminate a
desired portion of the object to be observed, via said curved beam
splitter, when the object is positioned along the observation axis
thereby facilitating generation of a substantially uniform
illumination field even when the illumination device is located
adjacent the object to be observed.
The invention also relates to the method of illuminating an object
to be observed by a camera along an observation axis extending from
the camera to the object, said method comprising the steps of:
utilizing a housing having two aligned apertures therein which are
both aligned with an observation axis; supporting a partially
reflective curved beam splitter within said housing between said
apertures and along the observation axis adjacent; arranging a
light source to cast light on a first surface of said beam
splitter; positioning a diffuser, inclined with respect to said
observation axis, between said curved beam splitter and said light
source for diffusing light from said light source as the light
passes through said diffuser to said curved beam splitter; supply
light, from said light source, through said diffuser to said curved
beam splitter; reflecting a portion of said light, via said curved
beam splitter, toward the object to be observed; allowing a portion
of light reflected back by said object to be observed to pass
through said curved beam splitter and be sensed by said camera
whereby said diffuser is sufficiently inclined with respect to the
observation axis so as only to be able, during use, to indirectly
illuminate a desired portion of the object to be observed, via said
curved beam splitter, when the object is positioned along the
observation axis.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described, by way of example, with
reference to the attached drawings, in which:
FIG. 1 is a diagrammatic illustration of an improved continuous
diffuse illumination device, equipped with an inspection camera and
other associated assembly equipment, providing light both along the
observation axis and at an angle to the observation axis according
to the present invention;
FIG. 2 is a diagrammatic top plan illustration of the continuous
diffuse illumination device of FIG. 1 prior to installation of the
inspection camera and other associated assembly equipment;
FIG. 3 is a diagrammatic perspective illustration of FIG. 1 prior
to installation of the inspection camera and other associated
assembly equipment;
FIG. 4 is a diagrammatic illustration, similar to that of FIG. 1,
showing a second embodiment of the attachment of the inspection
camera;
FIG. 5 is a diagrammatic illustration of a second embodiment of an
improved continuous diffuse illumination device, providing light
both along the observation axis and at an angle to the observation
axis, according to the present invention;
FIG. 6 is a diagrammatic illustration of a third embodiment of an
improved continuous diffuse illumination device, providing light
both along the observation axis and at an angle to the observation
axis, according to the present invention;
FIG. 7 is a diagrammatic illustration of a fourth embodiment of the
present invention;
FIG. 8 is a diagrammatic illustration showing an adaptor for the
fourth embodiment of FIG. 7 to provide all the advantages of one
embodiment of the present invention; FIG. 9 is a diagrammatic plan
view of a prior art illumination device showing the area which is
poorly and/or non-uniformly illuminated;
FIG. 10 is a perspective illustration of a curved beam splitter
according to the present invention;
FIG. 11 is a diagrammatic end-view cross-sectional illustration of
the object and camera using the curved beam splitter of FIG. 10 and
showing its optical effect;
FIG. 12 is a graph depicting the characteristics of a "diffuse"
light;
FIG. 13 is a graph of desired hemispheric lighting envelope;
FIG. 14 is a diagrammatic illustration of a further embodiment of
an improved continuous diffuse illumination device, equipped with
an inspection camera, in which the entire diffuser is "concealed"
from the object being observed;
FIG. 15 is a diagrammatic illustration of a still further
embodiment of an improved continuous diffuse illumination device,
equipped with an inspection camera, in which the entire diffuser is
"concealed" from the object being observed by the beam
splitter;
FIG. 16 is a diagrammatic view showing the parameters used to
calculate the size of the illumination device.
FIG. 17 is a diagrammatic view showing an arrangement for using a
flat beam splitter to illuminate an object to be observed;
FIG. 18 is a diagrammatic view showing the benefits of a curved
beam splitter to illuminate an object to be observed; and
FIG. 19 is a diagrammatic view showing the benefits of a curved
beam splitter to illuminate an object to be observed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning now to FIGS. 1-4, the first embodiment the invention will
now be described in detail.
As shown in FIGS. 1-4, a housing 18 encases the various components
of the continuous diffuse illumination device 2. The housing 18
comprises a first pair of spaced apart parallel side walls 19, a
second pair of spaced apart parallel side walls 20 and a roof wall
21 and a base wall 21'. An aperture 22 is formed in both the roof
wall 21 and the base wall 21' and the apertures 22 are concentric
with one another and located along the observation axis 16. The
housing accommodates therein at least one light source 28 adjacent
one of the side walls 19, a beam splitter 23 is located remote from
the light source 28 and positioned along the observation axis, a
light diffuser, shown generally as 24, is located between the light
source 28 and the beam splitter 23, and a light trap 26 is
supported by the side wall 19 opposite the side wall 19 adjacent
the light source 28. The arrangement of these components is such
that the light source 28 casts light upon the diffuser 24 which, in
turns, diffuses the light from the light source 28 and casts the
diffused light upon the beam splitter 23 which reflects a desired
portion of the diffused light toward the object 12. Any unreflected
light which passes through the beam splitter 23 is absorbed by the
light trap 26 located adjacent the beam splitter 23.
The beam splitter 23 has a partially reflective first surface 27. A
desired portion of the light, e.g. approximately half of the light,
from the diffuser 24 impacting upon the reflective first surface 27
of the beam splitter 23 is reflected toward the object 12, while
the remainder of the light passes through the beam splitter 23 and
is absorbed by the light trap 26. Likewise, a portion of the light
reflected back by the object 12 is transmitted toward and through
the beam splitter 23 along the observation axis 16 for viewing by
the camera 10. The light returned to the camera 10 is used to
determine the precise shape, orientation, and/or other
characteristics of the object 12. It is well known in this art how
to use of the light returned to the camera 10 to determine the
shape and orientation of the object 12, and thus a detail
description concerning the same is not provided herein.
An important aspect of the present invention is that at least a
first diffuser portion 25A is inclined with respect to the
observation axis 16. In all prior art known devices of which the
inventor is aware, the diffuser 24 is aligned substantially
parallel to the observation axis and thus provides direct lighting
of the object 12 to be observed. The first diffuser portion 25A,
according to the present invention, is inclined relative to the
observation axis, e.g. between an angle of about 5.degree. and
45.degree. and preferably approximately 25.degree. to 40.degree.
with respect to the observation axis, so that light diffused by the
first diffuser portion 25A cannot directly illuminate the object.
Accordingly, light from the first diffuser portion 25A is reflected
off either the inner roof wall 21 of the housing 18 or the beam
splitter 23 and thus indirectly illuminates the object 12 to be
observed. The inner surface of the roof wall 21 as well as the
inner surface of the side walls 20 of the housing 18 can be painted
with a white, gray, or another desired color or shade of paint or
some other diffusely reflective substance so as to provide desired
efficiency of reflection of the light diffused by the diffuser 24
onto the object to be observed to match the light reflected by the
diffuser 24.
Accordingly, the first diffuser portion 25A is concealed and is not
directly visible by the object 12 to be observed, i.e. the first
diffuser portion 25A is inclined such that it lies along a plane
indicated by dashed line 38 which is to the left of the object 12
to be observed and thus can not directly illuminate the object. The
second diffuser portion 25B extends vertically down from a second
edge of the first diffuser portion such that a portion of the light
passing through by that portion directly illuminates the object 12
and a remaining portion of the diffused light is reflected by the
inner surface of the side walls 19, 20 toward the object 12.
In this manner, a portion of the light diffused by the diffuser 24
directly illuminates the object 12 over a first range of incidence
angles and another portion of the light from the diffuser is
reflected by the reflective second surface 27 of the beam splitter
illuminating the object 12 over a second range of incidence
angles.
In order to cause light to be reflected to the object 12 from the
entire surface of the beam splitter 23, rather than being limited
to an area of the beam splitter surface bounded on its lower side
by a point reflecting a ray of light from the bottom edge of the
diffuser 24 to the object 12, as generally occurs with known
illumination devices, making use of beam splitter reflecting
diffuse light sources adjacent to the observation axis, the present
invention increases the length of the side walls 19, 20 so that the
spacing of the roof wall 21 from the base wall 21' is increased,
e.g. substantially doubled, over the proportional spacing of the
roof and base walls of the known illumination devices. The extended
side walls, according to the present invention, provide greater
housing surface area for reflecting the light passing through the
diffuser 24 and results in a substantially greater range of angle
of incident uniform lighting of the object 12 to be observed (FIG.
9).
Second diffuser portion 25B is made of a translucent diffusing
material selected of a material and thickness profile to pass
approximately as much light directly to the object 12 as is
reflected to the object 12 from the beam splitter 23 (see FIGS. 1,
4 and 6).
The light source 28 is either a single source of light (FIG. 6) in
the form of first 29 and second 30 light arrays (FIGS. 1 and 4) or
is first and second light members 29', 30' (FIG. 5). The diffuser
24 can likewise either be a single diffuser member, e.g. a curved
member having a radius of curvature approximately four times the
aperture width 22 for example, in which the curvature is designed
to approximate the first and second diffuser portions of the
diffuser. Alternatively, the diffuser 24 is in the form of first
and second diffuser portions 25A, 25B, e.g. first and second planar
diffuser members. The entire inner surface of the housing 18,
including the inner surface to the right of the diffuser 24 in
FIGS. 1 and 4, is preferably coated with a substance, e.g. paint,
which promotes directed reflection of the light generated by the
first and second light arrays 29, 30 and reflection of the light
diffused by the diffuser.
The present invention is also directed at increasing the apparent
brightness of the beam splitter so that the portion of the light
which is reflected, toward the object 12 to be observed, by the
beam splitter 23 closely matches the brightness of the light
reflected by the inner surfaces of the housing 18 whereby a more
uniform field of illumination is supplied to the object 12 and an
improved viewing of the object 12 by the camera 10 is achieved.
There are a number of ways in which the brightness equalization can
be accomplished. If a single light source is used to illuminate
both the first and second diffuser portions, then the first
diffuser portion 25A can be machined or modified to allow twice as
much light to pass therethrough than the second diffuser portion
25B. Alternatively, if two light sources are utilized, the
intensity of the light source associated with the first diffuser
portion 25A (see FIG. 5) can be accordingly increased by a light
intensity controller 25C or two or more light sources may be
associated with the first diffuser portion 25A and such two or more
light sources light sources may be positioned at different
angles.
FIG. 4 shows a second arrangement for mounting the camera to the
illumination device 2. In this embodiment, the camera 10 is a micro
television camera with a lens and the longitudinal axis of the
camera 10 extends substantially perpendicular to the observation
axis 16. The camera 10 is provided with a pair of mirrors M1 and M2
for reflecting the light returned along the observation axis 16.
For example, here mirrors M1 and M2 are oriented at angles selected
to cause the camera's optical axis and the observation axis to
substantially coincide. In this figure, the mirror M1 is oriented
at an angle of 64.5.degree. with respect to the observation axis 16
while the mirror M2 is oriented at angle of 112.5.degree. with
respect to the observation axis 16 thereby resulting in a
perpendicular reflection.
The embodiment of FIG. 5 is similar to the previous embodiment
except that the light arrays 29 and 30 are replaced with a pair of
fiber optic light guides 29' and 30'. Each one of the fiber optic
guides 29' and 30' is directed to shine light on a desired one of
the first and second diffuser portions. It is to be appreciated
that the number and orientation of the light sources, the light
arrays, the fiber optic guide, etc., can be varied depending upon
the application at hand.
FIG. 6 is a further embodiment of the present invention in which
both the diffuser and the light source have been modified. In this
embodiment, the diffuser 24 is a curved non-planar member. In
addition, the two light arrays 29 and 30 are replaced with a single
light source 28' which is a miniature fluorescent light array,
electro luminescent panel or fiber optic diffuser, for example. The
miniature fluorescent light array is powered by a pair of
conventional power supplies, with or without separate illumination
intensity controllers (not numbered), and, as such teaching is well
known in the art, a further description concerning such light is
not provided herein. A rear surface of the miniature fluorescent
light array 28' is provided with a planar reflector member 40 which
reflects the fluorescent light, directed toward the reflector
member 40, back toward the diffuser 24. The diffuser 24 is
preferably tapered at least at one end, preferably at both ends,
depending on the application, to equalize the amount of the light
that will pass through the diffuser 24. Typically, when a
fluorescent light is used, the generated light is brighter in the
central region of the fluorescent light and dimmer at the end
regions. The taper of the diffuser at both ends allows the light to
pass more readily through the diffuser and thereby compensate for
the lower amount of light available in the end regions of the
diffuser 24.
Turning now to FIG. 7, only a single planar diffuser member is
utilized and accommodated within the housing 18. The diffuser is
tilted at an angle of approximately 25.degree.-40.degree. with
respect to the observation axis 16 so as not to be visible by the
object 12, i.e. "concealed", when positioned for observation. In
addition, only a single light source 28 is employed. However, due
to the tilting of the diffuser 24, the diffuser cannot directly
illuminate the object 12 to be observed unless the object is placed
substantially in the aperture 22 provided in the base wall 21' of
the housing 18. Accordingly, the object 12 is not directly
illuminated, i.e. is "concealed", but receives a desired amount of
incident light reflected by the inner surfaces of the side walls
and inner roof wall of the housing and thereby results in a more
uniform lighting of the object 12 than prior art illumination
devices.
An adaptor to be utilized in combination with the illumination
device 2 of FIG. 7 will now be described with reference to FIG. 8.
The adaptor 54 comprises a housing 56 having an aperture 58 in the
end wall 60 thereof. A roof wall is not necessary and thus the top
of the adaptor may be open. The housing 56 contains a light source
62 and a second diffuser 64. The diffuser may extend substantially
parallel to the observation axis 16 or may be inclined a small
angle relative to that axis, e.g. a few degrees. The adaptor 54 is
connected to the base wall 21' of the illumination device 2, as
shown by the arrows in FIG. 8. The two components 2 and 54 are
securable to one another by any known securing mechanism, e.g.
glue, clamps, fasteners, etc., such that the apertures 22, 58 of
the two components 2, 54 are aligned along the observation axis 16.
The two secured components 2, 54 together function substantially
identical to the previous embodiments described above. The
preferred division between the first and the second components is
shown in FIGS. 7 and 8 and these two components may be sold
together or independently of one another.
The beam splitter 23 is preferably in the form of a mirror beam
splitter that is well known in the art, but it also could comprise
a cube or a membrane. The second surface 34 of the beam splitter 23
(FIG. 1), facing the camera 10, has an anti-reflection coating
disposed thereon to prevent stray light from being reflected toward
the camera 10 and thereby create a false image. Preferably,
magnesium chloride (MgCl) is used as the anti-reflection coating
for the beam splitter 23. It is to be appreciated that any other
suitable anti-reflection coating, that permits the camera 10 to
observe the object 12 through the beam splitter 23 free of a double
image or a ghost image, may be utilized on the second surface 34 of
the beam splitter 23.
The diffuser 24 may consist of a pair of planar plate members
formed of glass or plastic, as shown in FIGS. 1 and 4, each lying
in a different plane and having a surface which is translucent and
capable of diffusing light passing through the diffuser. The
diffuser 24 may alternatively be formed of an etched or ground
glass, or may be formed of opal glass having light scattering
centers of colloidal particles. Frosted glass, milky plastic or a
Murata screen may also be used. Murata screen is formed of a
diffusing synthetic plastic material.
It is important that the diffuser 24 have wide-angle diffuser
characteristics so that light cast thereon is evenly diffused by
the diffuser so that a substantially uniform intensity of light
passes through the diffuser for reflection toward the object 12 by
the beam splitter 23.
A variety of different light sources may be used as the light
arrays 28 and 29. For example, the light arrays 28 and 29 may be a
rectangular configuration having a plurality of bulbs evenly spaced
thereon. Alternatively, the light arrays may be incandescent fiber
optics, LEDs or fluorescent lights 5. The important requirement of
the light source is that it be capable of supplying a substantially
uniform intensity of light to the diffuser 24 so that the diffuser
24 may evenly diffuse the light received from the light source 28
and uniformly illuminate the object 12 both along the observation
axis and at an angle to the observation axis.
Preferably, the beam splitter 23 is disposed at an angle of
45.degree. with respect to the observation axis 16, however, it
will be appreciated that the angle of the beam splitter may be
varied, as desired, from a 45.degree. orientation and still
function in the desired manner. If the beam splitter 23 is located
at a 45.degree. orientation with respect to the observation axis
16, it is necessary to approximately double the length of the side
walls 19 and 20 to achieve substantially uniform illumination of
the object 12. If the orientation is varied from 45.degree.
orientation, the length of the side walls 19 and 20 would be
accordingly varied in order to provide uniform lighting of the
desired object 12. The length of the side walls is determined such
that the continuity of incident light, which falls on the object,
is substantially uniform. In addition, the size, shape and
orientation of the object 12 to be observed must be taken into
account, along with the tilt angle of the first diffuser portion
with respect to the observation axis, when determining the length
to the side walls.
For maximum uniformity of illumination, the beam splitter 23'
should be curved sufficiently (FIGS. 10 and 11) to eliminate the
beam splitter 23' from reflecting light, diffused by the first
diffuser portion 25A and reflected off the side walls located
between the beam splitter 23' and the first diffuser portion 25A,
toward the object 12 being observed, i.e. the beam splitter 23'
only reflects light directed toward the beam splitter and does not
reflect any light reflecting off the adjacent side walls 20, 21,
21'. In the case of an illumination device 2 having a 2 inch square
aperture and a beam splitter inclined at an angle of 45.degree.
with respect to the object, the calculated radius of curvature
required is 11.482 inches, which is just sufficient to cause
diverging rays to be collimated from the beam splitter 23' back to
the diffuser for a 2 inch square aperture. The required curvature
is a function of camera 10 and the part 12 distance, however the
true scale dimensions shown in FIG. 11 represent a good
approximation of a typical case. As a rule of thumb, then, the
radius of curvature of the beam splitter 23 should be slightly less
than 11.242/2=5.621 or, to be safe, a radius of about 5.5 times the
aperture dimension. This can achieved with a flexible beam splitter
by making the width of the beam splitter be between 101% and 102%
of its nominal flat width, and then fitting the oversize beam
splitter within its original nominal width holding fixture, thereby
flexing the beam splitter to the desired partially cylindrical
curvature.
FIG. 12 is a graph depicting the characteristics of a diffuse light
source while FIG. 13 depicts a lighting envelope which has
uniformity in a complete range of incidents of the lightening
envelope which is particularly adapted to determine the appearance
of specular (shiny) objects and surfaces. Variations of the
appearance of the specular objects and surfaces are minimized by
having a continuous unbroken field of illumination and a maximum
uniformity of the incident light.
The light trap 26 may consist of a planar panel defining a straight
wall parallel to the observation axis 16. The light trap 26 is
preferably of a flat black color so as to be capable of maximum
light absorption. Alternative, a portion of the inner surface of
the side wall 19 may be painted black, for example, to function as
the light trap. By locating the light trap in alignment with the
diffuser 24 and the beam splitter 23, light from the diffuser 24
passing through or reflected by the beam splitter 23 will be
absorbed by the light trap 26 and not be reflected or supplied to
the camera 10 where it could produce an erroneous signal.
A portion of the light diffused by the diffuser 24 will be
reflected by the beam splitter surface 27 in a uniform manner upon
the object 12. This uniform illumination of the object 12, in a
symmetrical relationship of light supplied along the observation
axis 16, permits the camera 10 to produce a highly accurate and
unambiguous image of the object 12 free of spurious glints and
shadows thereby to precisely view and determine the exact location,
orientation and other visual qualities of the object being
observed, particularly for shiny and uneven surfaces. This
facilitates accurate robotics control of the positioning and
manipulation of the object 12.
An important advantage achieved by the illumination device
according to the present invention, is that a substantially uniform
and diffuse lighting of the object 12 to be observed is achieved.
This is accomplished, in part, by adjusting the brightness of the
light supplied along the observation axis, diffused by the diffuser
24 and reflected by or supplied by the beam splitter 23, to be
substantially equal in brightness to the light which is reflected
by the inner surfaces of the housing side walls.
Turning now to FIG. 14, an improved continuous diffuse illumination
device 2 having a rectangular housing 18, a light source 28,
providing light along the observation axis a light trap 26 and a
beam splitter 23 is generally shown. The illumination device 2 is
also equipped with an inspection device 10, i.e. a camera, a
support table 14, a computer 4 and a robotics assembly or other
manufacturing apparatus 6. If desired, light provided off axis may
also be employed. As such components are similar or identical to
the previously discussed components of the invention, a further
detail discussion concerning the same is not again provide.
As with the previous embodiments, the housing 18 comprises a first
pair of spaced apart parallel side walls 19, a second pair of
spaced apart parallel side walls (not shown) and a roof wall 21 and
a base wall 21'. An aperture 22 is formed in both the roof wall 21
and the base wall 21' and the apertures 22 are concentric with one
another and located along the observation axis 16. The housing
accommodates therein the light source 28 adjacent one of the side
walls 19, the beam splitter 23 is located remote from the light
source 28 and positioned obliquely relative to and along the
observation axis, the light diffuser 24 is located between the
light source 28 and the beam splitter 23, and a light trap 26 is
supported by the side wall 19 opposite the side wall 19 adjacent
the light source 28. The arrangement of these components is such
that the light source 28 casts light upon the diffuser 24 which, in
turns, diffuses the light from the light source 28 and casts the
diffused light upon the beam splitter 23 which reflects a desired
portion of the diffused light toward the object 12. Any unreflected
light which passes through the beam splitter 23 is absorbed by the
light trap 26 located adjacent the beam splitter 23.
According to this embodiment, a diffuser 24 defines a plane P which
extends parallel to but is spaced from, i.e. does not intersect
with, the observation axis 16, i.e. at least the observation axis
defined between the inspection device 10 and the beam splitter 23.
That is, the diffuser 24 is recessed within the housing, i.e.
spaced from the aperture 22 of the housing 18, a desired distance
so as to prevent any ray of light emitted by the surface of the
diffuser 24 facing the beam splitter 23, when illuminated by the
light source 28, from directly illuminating any desired portion of
the object 12 to be observed. A line of sight 100 between a remote
portion of the object 12 to be observed and a remote portion of the
diffuser 24 is such that the entire diffuser 24 is completely
concealed or invisible from the desired portion of the object 12 to
be observed thereby preventing direct illumination of the object 12
to be observed. It is important to note that the object 12 to be
observed must be spaced from the aperture 22 a sufficient distance
so that the object to be observed 12 is to the right (as seen in
FIG. 14) of the line of sight 100. If the object 12 to be observed
is fairly large, this means that the object 12 must be spaced
further from the aperture 22 and this, in turn, may mean the
illumination device parameters must be increased so as to
sufficiently evenly illuminate the entire surface of the object 12
to be observed.
In order to achieve concealment of the diffuser in a typical
application, the diffuser 24 is mounted within the housing at least
0.5 inches from an adjacent edge E of the aperture 22, and
preferably spaced between about 0.5 inches and 8 inches from the
adjacent edge E of the aperture 22.
When designing an illumination device according to this embodiment
of the present invention, generally the following distance are
taken into consideration: the distance that the object 12 to be
observed is spaced from the aperture 22 (distance U) the overall
size (width) of the desired portion of the object 12 to be observed
(distance P), the size of the aperture 22 (distance W), the overall
height dimension of the diffuser 24 (distance X), and the distance
that the diffuser 24 is spaced from the aperture 22 (distance Y).
Generally, it is desirable to place the object 12 to be observed
fairly close, e.g. within a few inches or so, to the aperture 22 to
minimize the area required to be uniform illuminated.
As can be seen in FIG. 15, the position of the observation device
10 and the diffuser 24 and the light source 28 are switch. That is,
the diffused light will passes directly through the beam splitter
23 and the light reflected by the object 12 is reflected by the
beam splitter 23 toward the observation device 10 for viewing. In
this embodiment, the location of the light trap 26 is modified and
absorbs the diffused light which passes through the beam splitter
23 while the two aperture 22 are located adjacent one another and
extend normal to one another. According to this embodiment, the
beam splitter 23 completely shields the diffuser 24 from the object
12.
For flat planar surfaces (see FIG. 16), the following formula can
be used to calculate the proper minimum size of the illumination
device.
Minimum Illumination
Device Aperture Size (2P+A)-((P+A)(Z-LZ)/Z))
Where:
A=the entrance pupil diameter of the lens;
P=the object (field-of-view) width;
Z=the distance between the lens and the object measured along the
observation axis; and
LZ=distance from the top of illumination device to the top of
object measured along the observation axis. It is to be noted that
the first portion of the formula, namely (2P+A), alone describes
the proper size of the aperture of the illumination device when the
top of the illumination device is located at substantially the same
distance from the object 12 to be observed as the camera lens. The
second term, namely ((P+A)(Z-LZ)/Z)), specifies that the
illumination device becomes smaller in size as the top portion of
the illumination device 2 approaches the object 12 to be observed,
i.e. the illumination device 2 is located adjacent the object 12 to
be observed and remote from the camera lens.
The above formula is very useful for determining an illumination
device aperture size for viewing flat reflective planar surfaces.
For uneven surfaces, the inventor has not yet derived any precise
formula for calculating an optimum illumination geometry.
Therefore, a bit of trial and error may be required to find the
best solution to achieve for uniform illumination of the object.
Two useful rules of thumb for use in selecting an aperture size of
an illumination device for viewing uneven specular surfaces are to
be borne in mind. First, the illumination device should have an
aperture which is at least twice the width of the field of view of
the object to be observed. Secondly, a bottom portion of the
illumination device should be positioned as close to the object to
be observed as possible, i.e. adjacent the aperture 22 provided in
the base wall 21'. It should also be borne in mind that the further
the illumination device is from the object 12 to be observed, the
more the illumination device functions like a point light
source.
The diffuser 23 may be formed of treated glass, plastic, or some
other light translucent material capable of evenly diffusing light
cast upon the diffuser by the light source. The interior surface of
the housing 18 is painted or coated with a reflective substance
which is selected to reflect an amount of light which substantially
equal in intensity and character to the light reflected by the beam
splitter 23 so as to facilitate uniform illumination of the object
to be observed.
Turning now to FIG. 17, the simplest form of a coaxial diffuse
light source consists of a housing 18 which includes an aperture 22
formed in both the roof wall 21 and the base wall 21' and the two
apertures are spaced apart from but concentric with one another and
both located along the observation axis 16. The housing 18
accommodates at least one light source 28 therein, located adjacent
one of the side walls 19, and a beam splitter 23 is located remote
from the light source 28 and positioned along and centered with
respect to the observation axis 16. A light diffuser, shown
generally as element 24, is located between the light source 28 and
the beam splitter 23. A light trap 26 is located at the side wall
19' opposite the side wall 19 adjacent the light source 28.
For illuminating an uneven specular surface, the inventor has found
that the light source should provide as large a solid angle of
uniform diffuse coaxial light as possible. When a simple coaxial
light source, as shown in FIG. 17, is utilized at close range to
maximize the solid angle of illumination on the object to be
observed 12, the illumination field becomes highly non-uniform. In
particular, in the portion of the illumination field extending from
the far edge of the aperture 22, adjacent the light trap 26, to a
point on the beam splitter which reflects the bottom edge of the
diffuser 24 to the center of the object being observed 12, there is
no illumination of the object 12 at all. This non-illumination
region is labeled as "NI" in FIG. 17.
In the middle region of the illumination field, the light from the
diffuser 24 is reflected by the beam splitter 23 toward the object
to be observed 12 and this illumination region is labeled as "II"
in FIG. 17.
In the region of the illumination field located nearest to the
diffuser 24, the object 12 is both illuminated directly by the
diffuser 24 and by the reflected light from the beam splitter 23.
This maximum illumination region is indicated as "MI". Thus, the
traditionally geometry of employing a flat beam splitter 23,
located at an angle of 45.degree. with respect to the observation
axis 16, with a vertical diffuser 24 is incapable of providing a
uniform illumination field, except when the coaxial diffuse light
source 2 is spaced a great distance away from the object to be
observed 12.
The coaxial diffuse light source 2 of FIG. 18 provides a
substantially uniform illumination field even when the light source
2 is located closely adjacent the object to be observed 12, e.g.
within a few inches or so from the object 12. This is achieved by
first tilting the diffuser 24 relative to the observation axis 16.
The diffuser 24 can either be sufficiently spaced from the aperture
22 or be tilted, relative to the observation axis 16, at an angle
of between about 15.degree. to 75.degree., more preferably at an
angle of between about 30.degree. to 60.degree., and most
preferably at an angle of about 45.degree. or so. Secondly, the
flat planar beam splitter is replaced by a curved beam splitter 23C
so that the light provided by the light source 28 and passing
through diffuser 24C reflects off a surface of the beam splitter
23C and is directed at the object 12 to be observed. The curved
beam splitter 23C facilitates a larger solid angle of illumination
as well as a higher degree of uniformity across the illumination
field thereby improving the uniformity of the illumination of the
object 12 to be observed.
The curved beam splitter 23C can either have an elliptical shape or
other known curved profile, more preferably, an arcuate cylindrical
shape with a desired radius of curvature, i.e. the arcuate shape of
the curved beam splitter is a section from a cylinder. The term
"curved", as used herein, means a non-planar member and it is to be
understood that a single curved beam splitter may possible be
curved in two directions. It is to be appreciated that as the
radius of curvature of the beam splitter 23C increases, the height
of the co-axial diffuse light source correspondingly increases and
conversely, as the radius of curvature of the beam splitter 23C
decreases, the height of the co-axial diffuse light source 2 also
decreases. The height of the illumination source 2 is generally
shown by dimension H which distance comprises the spacing of the
apertures 22, from one another, when measured along the observation
axis 16 of the inspection system.
With reference to FIG. 19, the relationship between the radius of
curvature of the curved beam splitter 23C, the clear aperture of
the inspection system, and the size of the field-of-view FOV of the
object to be observed will now be provided. As can be seen in this
Figure, an observation cone OC, extending from the camera 10 to the
object to be observed 12 and indicated by a pair of dashed lines
forming a conical section, is defined by the inspection system. The
observation cone OC is dependent upon the size of the camera lens,
the size of the object to be observed and the relative spacing of
those two components from one another. The co-axial diffuse light
source 2 is selected and located, relative to those two components,
such that the aperture 22, formed in the base wall 21' of the
housing 18, is large enough so that the aperture 22 does not
interfere, in any way, with the observation cone OC defined between
the camera 10 and the object 12 whereby complete viewing of the
entire area of the object 12 by the camera 10 is facilitated. The
aperture 22, provided in the base wall 21', is commonly referred to
as the clear aperture of the inspection system. This aperture 22
typically has the shape of a square, a rectangle or a circle.
The curved beam splitter 23C is selected such that a light ray,
from any point on the object 12 to be observed, is reflected by the
beam splitter 23C to an exterior surface of the diffuser 24C.
Preferably, each light ray will only have a single bounce on the
reflective surface of the beam splitter 23 but it is possible for a
ray of light, reflected to the object 12, to have a double bounce
on the beam splitter 23, depending upon the radius of curvature of
the beam splitter, prior to being reflected at the object 12.
The radius of curvature of the curved beam splitter 23C, for a
cylindrical section, is defined by a central axis 100 which extends
perpendicular to the plane defined by the paper of FIG. 18 while
the radius of curvature, for an elliptical section, is defined by a
pair of foci, not shown, which extend perpendicular to the plane
defined by the paper of FIG. 18. The center, e.g. central axis 100,
or foci for the radius of curvature of the curved beam splitter
extend parallel to the planes defined by both the end walls 19, 19'
and the roof wall 21 and base walls 21'. Accordingly, the
cylindrical section of the curve beam splitter 23C extends
substantially perpendicular between the two opposed side walls 20.
The angle formed between the curve beam splitter and the
observation axis 16 varies along the curve beam splitter, e.g. a
first elongate straight edge portion FEP of said curved beam
splitter may form a small angle of about 35.degree. with respect to
the observation axis 16 while a second opposed elongate straight
edge portion SEP of said beam splitter 23C may extend substantially
perpendicular to the observation axis 16 or even at an angle
greater than 90.degree..
The radius of curvature of the curved beam splitter 23C typically
ranges between about 20 feet to about 0.3 inches. The radius of
curvature is generally about 1 to 3 time the minimum dimension of
the clear aperture of the illumination source, and most preferably
between about 1.8 times the diameter of the clear aperture of the
illumination source. A diagrammatic comparison of the height H2 of
an illumination device, incorporating a flat beam splitter, is also
shown in FIG. 19. It is readily apparent from this Figure that the
curved beam splitter 23C greatly reduces the overall height H1 of
the beam splitter while still providing a substantially uniform
illumination of the object to be observed 12.
The curved beam splitter is typically manufactured from a plastic
material and should be as thin as possible so that the beam
splitter does not distort or introduce a significant interference
to the image perceived by the camera 10, e.g. the plastic curved
beam splitter should have a thickness of between about 0.1 mm to
about 1.0 mm.
Since certain changes may be made in the above described
illumination device without departing from the spirit and scope of
the invention herein involved, it is intended that all matter
contained in the above description or shown in the accompanying
drawings shall be interpreted merely as examples illustrating the
inventive concept herein and shall not be construed as limiting the
invention.
* * * * *